In the conversion processes of sheet or coiled metals and nonmetals, including laminations, the area usage efficiency of the material is of primary importance and essential for economic and competitive operations. The economic aspects are of special relevance, particularly in the packaging industry which depends almost entirely on massive output quantities, wherein the efficiency of material usage has been recognized for many years as being very important, especially when individual blanks from which a given component is made are round or circular in shape.
If the conversion equipment contains only one blanking tool, the material utilization efficiency factor could be .pi./4 at best, when no shred allowance in the remaining skeleton is contemplated. Hence, in practice, the optimum material utilization factor would be around 75 percent, while leaving a manageable skeleton in the rectangular strips or straight-sided webs.
In the case of multi-tool equipment, wherein two or more blanks are simultaneously stamped, it is possible to employ a 60.degree. staggered pattern, which improves the material utilization factor to a figure of around 85 percent depending on the shred width in the remaining skeleton and the number of blanks accommodated across the width of the web. Such a figure is usually achieved when non-coated stock is employed, but can also be achieved when high volume justifies coil coating.
Over the past thirty years, can making industries started so-called primary scrolling of coiled materials to thereby produce sheets with scrolled leading and trailing edges. Such sheets could then be coated and secondarily scrolled, before being converted into components, to form single row, double row, or even multiple row strips. This practice results in a material utilization factor of about 85 percent depending on the shred width in the remaining skeleton.
In most applications of present can making practice, circular blanks are used for the manufacture of can end components or for providing "cups" suitable for so-called "two-piece cans", wherein the circular base and cylindrical wall are Joined without any seams. The material for the two-piece cans may be of a ferrous or non-ferrous character.
Usually the rolling mills finish the coils specified for deep drawing in such a way that so-called "earing" caused by the cupping operation is at a minimum. Earing is due to the anisotropy of the grain structure in the materials, the typical number of ears in ferrous materials being six. For circular blanks, earing results in the use of a larger diameter blank in order to provide an acceptably high cup. To avoid the use of larger diameter blanks, non-circular blanks could be used, such blanks providing additional material from the skeleton shred in the localities between the anticipated ears in the cup. However, blanking dies for such blanks are not practicable.
The established practice anticipates efficient utilization of wide coiled material using multi-die cuppers, which is practicable for high outputs only. To keep high utilization of material in case of low production outputs, wherein a single blanking or cupping tool is applicable, the coiled material needs to be processed twice, namely at first to cut the web into sheets, i.e., primary scrolling, and then secondly to cut the sheets into strips by secondary scrolling. This means more handling through costly additional equipment. Hence, single tool, low output mini-lines cannot compete successfully with the high speed multi-die production lines.